**5. Effects of digestate on crop yield**

On the bases of the plant reaction on the digestate treatment, plants could be classify into the sensitive (alfalfa, sunflower, soybean) and the non-sensitive (winter wheat, triticale,

Among the different organic wastes like compost, biogas residue, sewage sludge and different manures with and without mineral N, the biogas residue was more efficient for promoting the soil microbiological activity. The high amount of easy-degradable carbon increased the substrate induced respiration (SIR), which was enhanced by the higher carbon content resulted from the higher litter and root exudates of higher plant growth. In accordance with these results, the largest proportion of active microorganisms was found in the digestate treated samples (Odlare et al., 2008; Kirchmann, 1991). Similarly, the activity of invertase was significantly higher in the digestate treated samples than that in control ones

Besides the macro- and micronutrient content of digestate which are important not for the crops but for soil microorganisms too, it contains growth promoters and hormones, also. Therefore it could be used for stubble remains to facilitate their decomposing. Makádi et al. (2007) compared the effect of digestate and Phylazonit MC bacterial manure on the growth of silage maize (*Zea mays* L. 'Coralba') as a second crop after winter wheat and on the enzyme activities of soil. Digestate was used at the rate of 50% of the total N demand of silage maize while the Phylazonit MC was used at 5 L ha-1 dose. Their results of the changes

16/08/2006. 27/09/2006

Treatments Enzyme activity (mean±S.D.)

a) Control 5,6181,392a 3,7672,030b b) Phylazonit MC 7,4371,945a 4,0950,901b c) Phylazonit MC+digestate 6,6132,230a 1,5840,748a d) Digestate 6,0241,486a 6,2060,997c

a) Control 1,4680,118b 1,7970,289b b) Phylazonit MC 1,1600,144ab 1,4100,050a c) Phylazonit MC+digestate 0,9830,275a 1,2050,117a d) Digestate 1,9610,395c 1,2880,063a

Table 6. Invertase and catalase activities of soil on the 3rd and 9th week after digestate and Phylazonit MC treatment (*Data from Makádi et al., 2007*). a, b, c indexes mean the different

The maximum of the degradation of disaccharides, indicated by the invertase activity, was found in the 3rd week after Phylazonit MC treatment, while it was found only after the 9th week in the digestate treated soil samples. The Phylazonit MC contains only bacteria and promoting agents of bacterial activity for degrading the soil OM. Contrarily, in the digestate treated samples the degradation of disaccharides takes place at similar rate through 9 weeks because of the OM content of digestate used. Changes in catalase activity indicate the effect

On the bases of the plant reaction on the digestate treatment, plants could be classify into the sensitive (alfalfa, sunflower, soybean) and the non-sensitive (winter wheat, triticale,

(Makádi et al., 2006).

in enzyme activities are summarized in Table 6.

*Invertase activity (mg glucose 1 g-1soil 4 h-1)* 

*Catalase activity (mg O2 1 g-1 dry soil 1 h-1)* 

statistical groups according to Tukey's test (p<0.05).

**5. Effects of digestate on crop yield** 

of nutrient content of digestate to the increasing microbial metabolism.

sweet corn, silage maize) groups. The sensitive plants can be treated by digestate only in their certain life stages, for example, young alfalfa is very sensitive after sowing while old alfalfa is very sensitive before cutting. In the case of sensitive plants the burning effect of digestate can be observed but it follows a strong and quick recovering process. For the nonsensitive plants the digestate can be used in any developmental stage. It is favourable, because for example, in rainy period the digestate technically could not be applied (Makádi et al., 2008).

The right application rate of liquid or solid digestate depends on the plant nitrogen demand. It should be applied when plant N demand arises. This time for non-legume scpecies is the late winter and spring (Stinner et al., 2008). Similarly, Wulf et al. (2006) used 70% of the digestate in spring and 30% in autumn, while Makádi et al. (2008) and Nyord et al. (2008) split into two and three the applied rate through the vegetation period.

Because of its high available nutrient content, digestate application resulted in significantly higher aboveground biomass yields in the case of winter wheat and spring wheat than the farmyard manure and undigested slurry treatment. The effectiveness of a digestate depends on the composition of co-digestied material, the treated plant species and the treatment methodology. Co-digestion of different organic materials results in more effective digestate. (Möller et al., 2008; Stinner et al., 2008).

After the burning effect of digestate the soybean plants recovered and grew more, but lower sprouts. These sprouts were very productive, the number of pods was also higher in the treated samples, therefore the yield and thousand seed weight were also higher (Table 7, Makádi et al., 2006)


Table 7. Yield parameters of soybean after digestate treatment (*Data from Makádi et al., 2008).* a, b, c indexes mean the different statistical groups according to Tukey's test (p<0.05).

These yield parameters are close correlations with some soil parameters changing after digestate amendment. Increasing in important nutrient contents contribute to the better development of plants (Makádi et al., 2008b, Table 8).

Comparing the effect of liquid digestate and the equal quantity of water to the yield of sweet corn and silage maize, significantly higher yields were found in the digestate treatment. In this case the applied digestate on the bases of plants N demand was split into two parts (Makádi et al., 2006). That means that the favourable effects of digestate are caused by its soluble macro- and micronutrient content.

Digestate: A New Nutrient Source – Review 305

respectively. Changes in amino acid composition of test plants were also very favourable, because almost every essential and non-essential amino acid quantity was increased significantly after digestate treatment. In line with these results the oil content of the treated

> Carbohydrate (%)

Straw (100%) 21.56 28.81 10.43 0

biomanure 29.81 20.21 13.73 38.3

biomanure 33.57 21.45 7.96 55.7

biomanure 33.84 21.79 13.93 57.0

contents of mushroom (*Pleurotus sajor caju*). (*Data from Banik and Nandi, 2004*)

Table 10. Effect of supplementation of rice straw with solid digestate on major nutrient

Qi et al (2005) examined the effect of fermented waste as organic manure in cucumber and tomato production in North China. Before the vegetables transplantation, the diluted fermented residual dreg was applied 20-30 cm below the soil surface at a rate of 37,500 kg ha-1, while liquid digestate was sprinkled to the soil surface in three vegetables growing stages and on the vegetable leaves once time. They found increasing yield (18.4% and 17.8%) and vitamin C content (16.6% and 21.5%) of treated cucumber and tomato, respectively.

As the results show, the digestate application in solid or liquid form could result significant improvement in the quality of foods without damaging the environment, which is very

Sustainable recycling of organic wastes demands clear regulations of recycled wastes, the used recycling methods and the controlling of products. These regulation processes for the digestate are different in certain countries, respected the elaboration and the used limits.

In Hungary, the digestate is regarded as other non-hazardous waste if the ingestate does not contain sewage or sewage sludge, while in the presence of these materials the conditions of

In Scotland the BSI PAS110:2010 digestate quality assurance scheme is applied. If a digestate complies with the standards for the quality, the usage criteria and the certification system stated in the worked scheme, the Scottish Environment Protection Agency (SEPA) does not

In Swiss the digestate which suits the limits, can be used as soil conditioner and fertilizer in

In Germany the origin of the input materials determines the quality label of digestate product by biowaste and renewable energy crops. Digestates have to fulfil the minimum quality criteria for liquid and solid types which determine the minimum of nutrients and the

Lipid (%)

Increase of protein over control (%)

plants decreased significantly.

Straw + cowdung

Straw + poultry litter

Straw + jute caddis

Treatments Protein

(%)

important for the sustainable environment and healthy life.

**7. Legislation of digestate utilization in agriculture** 

the digestate utilisation depend on the quality of the given material.

apply the waste regulatory control for it.

"bio"-agriculture.


\* Correlation is significant at the 0.05 level; \*\* Correlation is significant at the 0.01 level.

Table 8. Correlations between soil and plant parameters in digestate treatment experiment. (*Data from Makádi et al., 2008b)*

Comparing the effect of digestate and a bacterial manure (Phylazonit MC, the experimental conditions can be found in the section 4.5). The Phylazonit MC treatment increased the green weight of silage maize by 47.18% while the digestate by 142.34%, comparing to the control. The results obtained can be seen in Table 9 (Makádi et al., 2007).


Table 9. Green weight of silage maize as a second crop after digestate and Phylazonit MC treatment of stubble. (*Data from Makádi et al., 2007*). a, b, c indexes mean the different statistical groups according to Tukey's test (p<0.05).

The positive effect of Phylazonit MC treatment was the result of its microbes, plant growth promoters and microelement content, while the favourable effect of digestate treatment was caused by its macro- and microelement and high water content and the increase of soluble macroelement content of soil because of the increased microbial activity.
